In the related art, a planetary gear mechanism is known as a transmission mechanism of rotative power. As an example of a planetary gear mechanism known in the related art, there is a technology including: a drive shaft (input shaft) adapted to be turned by drive force transmitted from a drive source; a sun gear attached to the drive shaft and adapted to be integrally rotated with the drive shaft; an internal gear provided coaxially with the sun gear via a predetermined space with the sun gear; a plurality of planetary gears provided at predetermined angular intervals in the space, and adapted to be engaged with the sun gear and the internal gear; a planetary carrier (rotary arm) provided coaxially with the sun gear and adapted to support the plurality of planetary gear in a freely turnable manner; and a driven shaft (output shaft) connected to the planetary carrier (refer to Patent Literature 1, for example). According the this structure, when the drive shaft is rotated while the internal gear in a fixed state, the planetary gears revolve around the sun gear while rotating on its own axis, and the driven shaft connected to the planetary carrier is rotated by this revolving motion.
According to the related art, the planetary carrier is normally provided at an end of the driven shaft and the plurality of planetary gears is provided in a freely turnable manner relative to the planetary carrier provided at the end (refer to Patent Literature 1, for example).
As a means to support the planetary gear in a freely turnable manner relative to the planetary carrier, in the related art, there is a case where a bearing hole is formed at the planetary carrier, the planetary gear having a through-hole formed in a rotary shaft direction is moved such that the bearing hole and the through-hole are aligned, and then the planetary gear is attached to the planetary carrier in a freely turnable manner by inserting a planetary pin (shaft pin) into the bearing hole and the through-hole. In the case of adopting this means, the through-hole is needed to be formed at a rotary center portion of each planetary gear.
Furthermore, as a means to attach the planetary gear in a freely turnable manner without preparing the planetary pin as a separate body, there is a case in the related art where a shaft portion is preliminarily formed integrally with a planetary gear body on each of both side surfaces of the planetary gear as a substitute of the planetary pin, and the planetary gear including the shaft portions is attached in a manner sandwiched between a pair of divided planetary carriers. In the case of adopting this means, the planetary carriers including bearing holes are preliminarily formed in a divided manner, and the planetary gear is sandwiched between the pair of the planetary carriers such that the shaft portions of the planetary gear are inserted into the bearing holes, and further the pair of divided planetary carriers is fastened by screwing or caulking, thereby attaching the planetary gear having the planetary pin to the planetary carrier in a freely turnable manner.
Since the planetary gear mechanism is used while being incorporated inside various kinds of mechanical devices such as a generator, a motor screw driver, and a washing machine, generally there is a demand to reduce volume thereof (size reduction). According to the technology disclosed in Patent Literature 1, the volume of an entire device is reduced by incorporating the planetary gear mechanism inside the motor rotor.